This invention relates in general to wireless communication systems, and more specifically to a method and apparatus for facilitating a classification of a baseband signal.
Some portable communication receivers are required to operate in communication systems using different transmission baud rates and different levels of modulation. Such receivers require a signal classifier to determine whether they are receiving a signal with which they can operate. The signal classifier generally comprises a baud rate detector and a modulation level detector.
Prior-art signal classifiers have utilized a zero-crossing detector to monitor a received down-converted baseband signal for baud rate detection. The baud rate detector has required the use of a peak and valley detector to establish thresholds for zero crossings. When local oscillator error is present, the peak and valley detector requires extra settling time before it can reliably estimate the zero point in the signal, thus decreasing battery life and increasing latency. For multi-level signaling, transitions occur which do not cross zero, and are therefore not detected by a zero-crossing detector. Also, the zero crossings are smeared by multi-level signals, and the performance of the detector degrades. In addition, prior-art signal classifiers have been known to false on noise. Prior-art signal classifiers also have required substantial computation for level detection.
Thus, what is needed is a method and apparatus in a signal classifier for facilitating a classification of a baseband signal. The method and apparatus preferably will require no peak and valley detector, will detect all transitions accurately without smearing, will not false on noise, and will minimize the computation required for level detection.
An aspect of the present invention is a method in a signal classifier for facilitating a classification of a baseband digital signal. The method comprises the steps of receiving the baseband digital signal; and delaying the baseband digital signal by a symbol duration, thereby generating a delayed baseband digital signal. The method further comprises the steps of adding the baseband digital signal to the delayed baseband digital signal, thereby generating a summed signal; and dividing the summed signal by two, thereby generating a threshold signal. The method also includes the steps of delaying the baseband digital signal by one-half the symbol duration, thereby generating a half-delayed signal; and subtracting the threshold signal from the half-delayed signal, thereby generating a candidate signal. In addition, the method includes the steps of searching for a zero crossing in the candidate signal, and generating a pulse in response to finding the zero crossing.
Another aspect of the present invention is a signal classifier for facilitating a classification of a baseband signal. The signal classifier comprises a processor for receiving and processing the baseband signal. The processor is arranged and programmed to digitize the baseband signal, thereby generating a baseband digital signal, and to delay the baseband digital signal by a symbol duration, thereby generating a delayed baseband digital signal. The processor is further arranged and programmed to add the baseband digital signal to the delayed baseband digital signal, thereby generating a summed signal; and to divide the summed signal by two, thereby generating a threshold signal. The processor is also arranged and programmed to delay the baseband digital signal by one-half the symbol duration, thereby generating a half-delayed signal; and to subtract the threshold signal from the half-delayed signal, thereby generating a candidate signal. In addition, the processor is arranged and programmed to search for a zero crossing in the candidate signal, and to generate a pulse in response to finding the zero crossing.
Another aspect of the present invention is a receiver for facilitating a classification of a baseband signal. The receiver comprises a receiver front end for down-converting a received modulated signal to produce the baseband signal, and a signal classifier for facilitating a classification of the baseband signal. The signal classifier comprises a processor for receiving and processing the baseband signal. The processor is arranged and programmed to digitize the baseband signal, thereby generating a baseband digital signal, and to delay the baseband digital signal by a symbol duration, thereby generating a delayed baseband digital signal. The processor is further arranged and programmed to add the baseband digital signal to the delayed baseband digital signal, thereby generating a summed signal; and to divide the summed signal by two, thereby generating a threshold signal. The processor is also arranged and programmed to delay the baseband digital signal by one-half the symbol duration, thereby generating a half-delayed signal; and to subtract the threshold signal from the half-delayed signal, thereby generating a candidate signal. In addition, the processor is arranged and programmed to search for a zero crossing in the candidate signal, and to generate a pulse in response to finding the zero crossing.